Now click the Reviews tab and look for a review by a poster going under the name "Dr Holly". She says:

... though most magnesium supplements passed their testing, this one failed, as well as a brand called Total Nutrition.

I'm tossing this in the trash, sad to say. Here is what consumerlab has to say:

* Peter Gillham's Natural Vitality® Natural Calm, a powder, was found to contain 0.295 mcg of lead per teaspoon. It suggested a daily dose ranging from 1/2 teaspoon to 3 teaspoons per day which, at the higher end of the range, would exceed the State of California's limit of 0.5 mcg of lead – above which a warning label is required. Such lead exposure can be easily avoided when taking magnesium, as evidenced by the many other products that did not exceed this limit.

Out of interest I looked up which foods are high in magnesium. I think food sources are always better, but I don't think there are many good ones for magnesium. I may be wrong here, but one of the problems I understand is that stress depletes magnesium, and of course modern life is stressful (not actually dangerous but time-obsessed and hurried and continually frustrating in small ways).

There seems also no doubt that people who are lucky enough to live in areas where the water supply is naturally high in magnesium have good bones.

Kind of interesting, though. I started looking around and finding out a little more. That stress depletes it seems to be true. I had heard it tended to be depleted in soil—according to one lady over at the WAPF site that's quite true for some interesting reasons:

First of all, modern agricultural methods favor the universal use of NPK fertilizers (nitrogen, phosphorus, and potassium). Both potassium and phosphorus are antagonists of magnesium in the soil, and on calcareous soils create a relative magnesium deficiency (the magnesium present is bound and therefore unavailable to the crop). On sandy or loamy soils that are slightly acid, an actual magnesium deficiency often exists, as the magnesium leaches from the soil and is also unavailable to the crop. This leaching also occurs in response to acid rain. ...

Oops. If that's right, two of the problems are of our own making, viz., artificial fertilizers and acid rain. Of course, with current population sizes, crops will tend to be grown intensively, and everyone wants power stations and motor vehicles ... and here we are.

From the sound of it, it would be difficult under current circumstances to get enough from food, because current agricultural, storage, and processing methods militate against it.

The same source quotes the Food Commission in the UK on falls in minerals in dairy products between 1940 and 2002:

Mineral declines in dairy products showed that milk lost 60 percent of its iron, 2 percent of its calcium, and 21 percent of its magnesium. Compared to 1940, currently “[m]ost cheeses showed a fall in magnesium and calcium levels. According to the analysis, cheddar provides 9 percent less calcium today, 38 percent less magnesium and 47 percent less iron, while parmesan shows the steepest drop in nutrients, with magnesium levels down by 70 percent.”

Originally Posted by MvEssen

Cacao also has a decent amount of magnesium I think.

Unfortunately, it also has phytates. And as for those ...

Tannins, oxalates, and phytic acid all bind with magnesium, making it unavailable to the body unless extra care is taken to neutralize some of these compounds during food preparation.

AFAIK, the Aztec chocolatl was some kind of fermented drink, a chocolate beer, as it were.